[maven-release-plugin] prepare for next development iteration

git-svn-id: https://svn.apache.org/repos/asf/sling/trunk@1579462 13f79535-47bb-0310-9956-ffa450edef68
switch to api snapshot until release is out

git-svn-id: https://svn.apache.org/repos/asf/sling/trunk@1579464 13f79535-47bb-0310-9956-ffa450edef68
Use latest snapshot

git-svn-id: https://svn.apache.org/repos/asf/sling/trunk@1579469 13f79535-47bb-0310-9956-ffa450edef68
Use released Sling API

git-svn-id: https://svn.apache.org/repos/asf/sling/trunk@1579470 13f79535-47bb-0310-9956-ffa450edef68